1. Field of the Invention
The present invention relates generally to an actuator positioning system in a direct access storage device (DASD) and more particularly to a phase plane trajectory trough method and apparatus for fast settling of a data transducer in a disk file.
2. Description of the Prior Art
Computers often include auxiliary memory storage units having media on which data can be written and from which data can be read for later use. Disk drive units incorporating stacked, commonly rotated rigid magnetic disks are used for storage of data in magnetic form on the disk surfaces. Data are recorded in concentric, radially spaced data information tracks arrayed on the surfaces of the disks. Transducer heads driven in a path toward and away from the drive axis write data to the disks and read data from the disks.
All DASD units must have a method to position each data head over the proper radial location to write a track and again, to position it very close to the same location to read the track. With the higher-level files using a voice coil type of actuator, a feedback mechanism must be provided to locate and stably hold the head on a given track.
Historically in actuator control systems, the settle process that occurs during an access operation has been a very difficult process for an actuator servo system to control with reasonable consistency. This difficulty can be caused by many things that introduce variability into the settle process. For example, temperature can affect changes in many system parameters, such as, actuator torque constant, actuator bearing stiffness, actuator material stiffness and actuator flex cable bias. Actuator flex cable bias differences occur at various actuator locations. Nonlinearities occur in actuator bearings and flex cable spring constants. Access distance and external forces, such as windage and vibration, introduce variability into the settle process.
The settle process that occurs during an access operation in an actuator control system has a direct effect on the overall access performance of that system. If the actuator control system has difficulties in settling the actuator to the desired position, then the time required to perform a complete access operation increases, which can result in undesirable throughput performance.
Traditional actuator control methods typically use proportional-integral-derivative (PID) controllers to move an actuator to a desired position. However, PID controllers inherently exhibit a slow response when designed to minimize overshoot, or the PID controllers exhibit overshoot when designed to provide for a fast response. The conventional PID controller cannot consistently provide both a fast response and minimal overshoot. Known actuator control methods consume a significant amount of microprocessor memory and time, which limits their use to fairly low sample rate systems.
A need exists for a method that can be used to improve the settle process in an actuator control system so that a faster and more consistent settle control action is achieved, and which also results in improved throughput performance. In addition, it is desirable that such a method does not require considerable microprocessor memory or instruction execution time to implement.